Electron discharge tube



Jan 10, 1939. G. SCHUBERT ET AL ,1 2

' ELECTRON DISCHARGE TUBE Filed Feb. 5, 1938 INVENTORS, GEO/PG SCHUBERT.ULRICH mwc/r.

BY ERA/S7 RUSK/4 W TORN s.

Patented Jan. 10, 1939 PATENT OFFIE ELECTRON DISCHARGE TUBE GeorgSchubert,

Berlin- Zehlendorf,

Ulrich Knick, Steglitz, and Ernst Ruska, Spandau,

Germany, Aktiengesellschaft, Germany Application February In Germany 2Claims.

It may be necessary to shield, in part or completely, individualelectrodes or groups of electrodes in photoelectric multipliers forvarious, such as for instance electrical reasons. This,

however, complicates the forming of the tube because the screened-offelectrodes are not soreadily accessible to oxygen or caesium as theunscreened electrodes, and the oxidation of the screened electrodescannot be observed. Therefore, special tubulations for the introductionof caesium to such a screened-off group of electrodes must be providedfor the forming, or the attempt must be made to maintain certaindifferences in temperature between the screened-off and the openelectrodes. However, the disadvantage still remains that the degree ofoxidation of the screened electrodes cannot be observed.

These defects may be overcome if the screening device is carried outaccording to the invention in such a manner that it may be opened andclosed in vacuum. The forming may then take place when the screen isopen, whereby all of the above-mentioned diificulties during the formingprocess are eliminated. After the process is completed screening isclosed, while the tube is in an evacuated condition. The covering devicecan be operated, for instance, magnetically or by relieving the tensionon a spring, for instance, by a fuse wire or bimetallic spring, or byinertia or gravity, respectively. It is preferable to provide such alocking device which may maintain the movable part in a fixed positionfor operation of the tube and which cannot be opened at all or only bythe same means, as above mentioned. A further advantage of the deviceaccording to the invention is the possibility of measuring thephotcsensitivity or secondary emission ratio after the forming of thetube by illumination or bombardment by electrons.

As an example, the application of the invention in an image analyzingtube with a stationary aperture and secondary emission amplificationwill be described. In the device according to Farnsworth illustrated inthe drawing, the lens 6 projects an image of the object to betransmitted upon the photocathode l. The electron image therebyproduced, and of which the current density distribution in spacecorresponds to the values of light intensity of the optical image, isscanned across the aperture 8 by means of deflection fields. Thesecondary emitting electrodes i of the electron multiplier aredisposedin a screened cylindrical metal housing 3-4 which is placed in thecylindrical tube diametrically in front of the window through which theassignors to Zehlendorf, near Berlin,

the firm of Fernseh 5, 1938, Serial No. 189,012 February 4, 1937 lightfalls. According to the invention, this metallic housing is interruptedby an aperture, leaving the electrodes free, and a movable tube 5 isprovided which may be moved over the aperture of the screened cylinderby means of gravity after the tube is sealed from the pump and whichtube is held in the aforementioned position indicated by the dottedlines in the drawing. In order to secure good electrical contact betweenthe screened cylinder and the movable tube 5, the two; are connected bymeans of a thin flexible conductor 9. A guide it provides turning of thetube 5 while it is slid over the screened cylinder 3@ in order to bringan aperture II in the tube into such a position that it may serve as anaperture through which the photoelectrons enter into the cylinder 3-4.Upon striking the inner wall of that portion of the cylinder designed byreference numeral 3, such electrons as are refiected and such as may besecondarily emitted, will be attracted to the first electrode of theelectron multiplier.

A screen provided with a movable portion may also be used to advantagein such cases where the forming of the surfaces is to take place in ascreened-off space for certain reasons while the electrodes lie openduring the operation of the tube. The above disadvantages may then beapplied in an opposite manner.

We claim:

1. A cathode ray device comprising an envelope housing a photosensitivecathode at one end thereof, electron receiving means at the opposite endof said envelope, electron multiplier means comprising a plurality ofsecondary emissive electrodes and slidable hollow shielding means inalinement with said electrodes initially displaced therefrom to enablesensitizing said electrodes to render them secondary emissive andslidable over said electrodes to shield them against direct flow theretoof electrons from said cathode.

2. An electron discharge device comprising a cathode and a cooperatingelectron receiving means spaced therefrom, an electron multiplier havingan electrode electronically exposed to said electron receiving means, aslidable hollow shield electrically connected to said electron receivingmeans and initially displaced from said electron multiplier electrode toenable sensitizing said electrode to render it secondary emissive andslidable over said electrode to thereafter limit the exposure of saidelectrode to said electron receiving means only.

GEORG SCHUBERT. ULRICH KNICK. ERNST RUSKA.

